In recent years, a capsule endoscope having an imaging function and a radio communication function appears in a field of endoscope. After being swallowed by a patient, i.e., a subject, from the mouth for an observation (examination), the capsule endoscope travels through inside internal organs (body cavities) such as stomach and small intestine following peristaltic movements and sequentially captures images using the imaging function until naturally discharged from a living body (human body) of the subject, in other word, during an observation period.
During the observation period in which the capsule endoscope travels through the internal organs, the capsule endoscope captures images in the body cavities thereby obtaining image data, and sequentially transmits the image data to a receiving apparatus provided outside the subject body using the radio communication function. The image data received is accumulated in a memory inside the receiving apparatus. When the subject carries the receiving apparatus equipped with the radio communication function and the memory function, the subject can move freely without inconveniences even after swallowing the capsule endoscope and before discharging the same, i.e., even during the observation period. After the observation finishes, a doctor or a nurse can display images inside the body cavities on a display unit or the like based on the image data accumulated in the memory of the receiving apparatus, and make diagnosis.
Generally, the receiving apparatus includes plural antennas for receiving image signals transmitted from the capsule endoscope. The antennas are dispersedly arranged outside the subject body and one with a less error in image signal reception is selected for the reception via switching. For example, Patent Document 1 describes a receiver which selects one of plural antennas arranged outside the subject body by switching and locates a capsule endoscope, which sends image signals, inside the subject body based on strength of an electric field received by each antenna.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-19111